1. Field of Invention
This invention relates generally to safety devices for school buses, and more particularly to a control system therefor which when the door of the bus is opened to unload or load passengers, this causes a stop sign or a crossing arm to swing out, and when the bus door is closed, the sign or arm is then caused to return to its retracted position.
2. Status of Prior Art
School buses pick up or discharge children attending a school serviced by the bus at various points along a route running through the community in which the school is situated. As a safety measure, school buses have for many years been equipped with a stop sign mechanism under the control of the bus driver, the mechanism acting to swing out the stop sign from its normally retracted position against the side of the bus to an outstretched position to provide a signal alerting drivers of nearby vehicles that children are entering or alighting the bus. U.S. Pat. Nos. 2,384,689 and 3,094,683 are illustrative of manually-operated school bus sign devices, while U.S. Pat. No. 2,252,529 discloses a hydraulically-operated school bus sign.
It is also known to provide motor-operated school bus signs, such apparatus being illustrated in U.S. Pat. Nos. 2,281,717 and 4,138,668. Of greatest prior art interest in this regard is the 1982 U.S. Pat. No. 4,339,744 to Latta, Jr. In this patent, the stop sign mounted on the side of the bus is operated by a unidirectional DC motor and a linkage associated with the sign. This linkage in conjunction with limit switches acts to deploy and retract the stop sign.
Also of prior art interest is the U.S. Pat. No. 4,697,541 to Wicker, wherein a school bus is provided with a crossing arm attached to the front bumpers of the bus for movement between a retracted position alongside the bumper to an extended position projecting outwardly from the bumper to protect children walking in front of the bus.
The concern of the present invention is generally with safety devices for school buses of the stop sign or crossing arm type, and in particular with the control system for actuating these devices.
In the control system disclosed in the Reavell U.S. Pat. No. 4,766,413, a hinged stop sign for a school bus is driven by a unidirectional DC motor through an eccentric drive and a link arm having associated therewith two normally closed limit switches. In the course of a motor operating cycle, the stop sign swings out to its fully outstretched position, at which point one limit switch is caused to open, and then returns to its retracted position, at which point the other limit switch opens. The limit switches are included in a control circuit which supplies power to the motor.
The control circuit is responsive to a door switch associated with the bus door so that when the door is opened, the door switch is then closed, and power is supplied to the motor through one closed limit switch until the sign reaches its outstretched position, at which point this limit switch opens to cut off the motor. When the door is closed and the door switch is then open, power is supplied to the motor through the other closed limit switch until the sign reaches its retracted position, at which point this limit switch opens to cut off the motor. Thus the operation of the sign is coordinated with that of the bus door to provide a stop signal when the need therefor arises. Similar limit or microswitch arrangements are included in the control circuits disclosed in the above-identified Latta, Jr., patent.
The use of limit switches in a control system for a school bus safety device has certain practical drawbacks. Such switches are highly sensitive and therefore may respond falsely to vibratory forces. Thus where as in the prior Reavell U.S. Pat. No. 4,766,413, the microswitches are associated with a link arm coupled to a stop sign, should the sign vibrate, these vibrations will be transferred to the link arm and cause improper actuation of the switches.
Also, in typical safety device control circuits using limit switches, the switches are interposed between the motor and the positive or high side of the power supply. Should either of the limit switches become grounded as a result of a circuit defect, or because of water seepage into the control box mounted on the exterior of the bus, the resultant heavy current flow may overheat the circuit and give rise to a fire. This condition is scarcely conducive to the safety of the children carried by the school bus.